The present invention relates to preventing lightup in holes of an electrostatic chuck (“ESC”) feeding the backside of a wafer during processing or cleaning operations.
In semiconductor material processing facilities, plasma processing chambers are often used for operations such as etching and deposition. Usually, a semiconductor wafer is placed on an ESC where it is held during the processing. An ESC may have holes for admitting gasses to the clamped side of the wafer to facilitate cooling or heating of the wafer, or to purge hole features in the ESC during plasma cleaning of the ESC surface.
Where low pressure gasses are present within ESC holes, and where electric voltage gradients are present, a form of glow discharge, or arcing may occur, which may be detrimental to the process. U.S. Pat. No. 6,033,585 discusses avoidance of lightup in gas distribution holes within an ESC by providing a circuitous path for the distributed gasses, wherein lightup is prevented. U.S. Pat. No. 8,503,151 discusses the use of a dielectric arrestor insert to prevent arcing and lightup.
As applied to gas holes in electrostatic chucks, U.S. Pat. No. 6,108,189 purports to address the issue of arcing and lightup by coating the inside of holes in the electrostatic chuck with a dielectric material. However, this does not reduce the path length of gas molecules within the holes. It also discusses using a dielectric layer at the opening of the holes in the electrostatic chuck facing the wafer. A problem with using a single channel through a top dielectric layer is that depending on the design, this top layer may be thick enough so that a single channel through it might cause lightup.
The U.S. Pat. No. 6,108,189 patent describes another solution of using a porous plug of dielectric material in the top layer of the electrostatic chuck, so that gas takes a tortuous path through the hole in the electrostatic chuck. Many such configurations, however, can leave gaps which have the potential to lead to lightup. In addition, such porous plugs may be difficult and complicated to manufacture and align.
There is a need for a better system and method for preventing lightup in an electrostatic chuck, which is effective, eliminates long stretches of open space where particles may be accelerated, and is easy to manufacture in light of current designs for electrostatic chucks.